This invention relates to solid aluminum hydroxide compositions and to a method for preparing them. The compositions of the invention are readily filterable when slurried, and readily redissolvable in acidic solutions, and retain these properties for much longer periods of storage in air than previously known solid aluminum hydroxide preparations.
When freshly prepared as an amorphous solid, aluminum hydroxide can be fairly easily redissolved in acidic solutions, such as aluminum sulfate (alum) solutions, a property which is utilized in many processes for the production of basic aluminum complexes for use in water treatment. Upon standing, however, the structure of the solid aluminum hydroxide changes, such that after 7 to 14 days the aluminum hydroxide is essentially insoluble in the alum solutions. This old aluminum hydroxide must then be reprocessed by adding a strong mineral acid, such as H.sub.2 SO.sub.4 and then reforming the Al(OH).sub.3 if it is to be used, and may in fact be simply discarded.
Furthermore, because of the amorphous structure of known soluble aluminum hydroxide compositions, this material generally forms a sludge or gel upon addition of water, and is not easily handled. In particular these sludges are difficult to transport, and difficult to filter. This latter difficulty complicates removal of sodium sulfate which is desirable for the production of low sulfate basic aluminum complexes.
It is therefore an object of this invention to provide aluminum hydroxide compositions that retain their solubility over substantially longer periods than known aluminum hydroxide compositions.
It is a further object of this invention to provide soluble aluminum hydroxide compositions in the form of a granular, free flowing material.
It is another object of this invention to provide a simple and convenient method of making the novel aluminum hydroxide compositions.